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A deep dive into Apple’s UDID replacement Advertising ID and how it affects user privacy

Over a year ago, Apple started warning developers to stop referencing the Universal Device Identifier (UDID) in their apps, eventually rejecting them altogether. This caused a bit of a stir because it was the primary method by which ad networks tracked users and devices for the purpose of selling advertising.

The issue with UDID as an identifier for ad tracking is that you can’t change it. You get one with a device and it’s with you as long as you have that device, period. This is useful on the development side of things, as Apple uses it to help provision devices, but it becomes too powerful a tool when used for other things like advertising. That’s why Apple introduced the non-permanent Advertising ID and the ability to turn that ID off completely if you didn’t want to be tracked by advertisers.